The invention relates to a threaded pairing comprising two threaded parts. This threaded pairing is hermetically sealed by a sealing compound between the parts. Such threaded pairings are used principally in applications where a steady turning angle must be warranted in respect to a discrete axial positioning between the threaded parts and the resulting joint must also be leak-proof and resistant to distortion.
There are a number of different state of the art technological solutions. In the case of a customary threaded pairing in line with the classification F16B of the international Patent Classification (IPC) the two threaded parts are generally screwed into each other against an axial stop of one of the threaded parts, which is used with an admissible axial tension to create a positively fitting and frictionally actuated joint. This arises both from the positive interlocking of the thread flanks and from pitting the respective thread flanks against each other.
A sealed threaded joint is disclosed, for example, in the publication DE-U1-29604120. In this an essentially hollow cylindrical receiving section adjoins the hollow cylindrical part of a threaded sleeve, so that a step in the transition forms a sealing device which serves as a receptacle for the assigned counterpart, and with either elastic or plastic deformation also ensures a sealing. In such a threaded joint, no additional turning of one of the threaded parts beyond the torsion angle determined by the axial stop is possible as the axial limit stop ensures clear positioning and any additional turning would lead either to an inadmissible loosening or excessive tensioning. The positional anomalies of the threaded parts against each other prevent their free rotation and also result in a fixed axial position determined by the stop. Such rigid positioning of the threaded parts in relation to each other makes it necessary, for example, to carry out extensive adjustment work in serial production, i.e. to create adjustable limit stops. This leads to unnecessary production costs.
It is also known that frictionally-connected wedge-shaped union or sealing devices are used for the transmission of axial traction or fluid power. The publication DE4439250C1 discloses, for example, a sealing element for pipes with a wedge-shaped lip, which when used together with an axial tapered collar creates a releasable frictionally-connected joint and seal. Due to the positional allocation of the parts to be connected, such frictionally-connected joints are mostly insufficiently fixed and frequently difficult or even impossible to release. In particular, it is not possible to adjust the assigned positioning.
So-called "floating fittings" are also known. As these only provide for a positive positioning of the threaded parts, without any tensioning there is a certain play between the threaded parts. Such a positioning is only determined by a positive allocation of the threaded parts and thus it is necessary to secure it, for example against turning. However, in many applications such play is not admissible.
Applying sealing compounds in the screw thread is a known method for sealing threaded pairings. In most cases, such sealing compounds are applied as liquids or pastes to the screw thread prior to the final assembly and cured subsequently. This ensures that the screw thread itself does not constitute an opening, and at the same time the positioning is secured by fixing the threaded pairing.
However, in a customary positively-fitting and frictionally-connected joint it is not possible to seal with a suitable sealing compound, as the compound cannot continuously fill the gap between the supporting flanks of the compressed threaded pairings. This is due to the one-sided tensioning of the threaded pairing and the resulting stress. As a result, the small cracks in the sealing compound and the ruptures in the flanks expand over time and the threaded pairing becomes more permeable. For this reason, this method of filling up the screw thread, which only constitutes an adequately filling between the free flanks, is only used for fixing the position with the application of an adhesive. A sealing effect cannot be achieved.
On the other hand, suitable sealing compounds can be successfully used as seals for "floating fittings", as in this application both sides of the screw thread can be adequately filled with sealing compound. However, the threaded parts are not positioned directly against each other, but instead are softly embedded in the sealing compound. This results in such components being considerably less rigid than is customary for threaded joints. This degree of rigidity is insufficient for many applications.